Lipid Bilayer Passive Area Regulation in Response to Fluid Flows

Abstract

Mechanotransduction is the cellular process in which mechanical stimuli are converted into biochemical signals to induce specific cellular responses, enabling the cell to sense and respond to mechanical forces. Although many cells exhibit this behavior, vascular endothelial cells (ECs) are of considerable interest as they effectively respond to fluid shear stress, adapting their morphology, functions and gene expression to maintain the homeostasis of the vascular system. Fundamentally, these processes rely on the transduction of intracellular signals through the lipid membrane, and several studies have already demonstrated that shear stress induces significant changes in lipid order and viscosity of ECs plasma membrane. Despite such extensive study, the underlying molecular mechanisms that control this change to membrane lipid order and viscosity remain unclear. Supported lipid bilayers provide an ideal platform for the investigation of the molecular mechanisms behind shear induced biophysical changes in membrane structure. As a minimal model system, they are suited for isolating the physical role of lipid bilayer in membrane shear response, in the absence of active biological processes. Here, combining microfluidics and fluorescence microscopy, we examine how the application of controlled fluid flows on supported lipid bilayer patches alters their physical properties. We observe a reversible and significant ∼10% increase in SLB area (when physiological shear stresses of 1-2 Pa are applied). Such area fluctuations have been a previously suggested response to fluid shear stress but have not directly observed. Furthermore, we determine how these membrane area fluctuations in response to fluid flows depend on lipid composition and surface roughness. Identifying the origin of such flow-induced changes in membrane structure could reveal an underlying mechanism utilized by biology to sense and direct changes in membrane order and viscosity in response to shear flows.